Mouse adrenocortical tumor cells (Y-1) will be studied in monolayer culture. Mitochondrial cytochrome P-450 will be purified and characterized for physical and enzymatic properties which will be compared with those of normal mouse adrenal. Tubulin (colchicine-binding protein) already found in the tumor cells will be purified and characterized and actin will be sought and purified (if found). The role of microfilaments in the response to ACTH will be studied by fluorescent-labeled antibodies in cells treated with ACTH and in controls. The cell cycle of the tumor cells will be determined and the response to ACTH at various stages in the cycle will be compared; the influence of ACTH on the cycle will be examined. It is proposed to study the contribution(s) of host mice to enhancing the steroidogenic activity of tumor cells injected into such mice, by determining whether the endocrine glands or the plasma of the host (or both) are responsible for this effect.